VGO is a hydrocarbon fraction that may be converted into higher value hydrocarbon fractions such as diesel fuel, jet fuel, naphtha, gasoline, and other lower boiling fractions in refining processes such as hydrocracking and fluid catalytic cracking (FCC). However, VGO and other heavy hydrocarbons such as de-asphalted oil (DAO) are known to contain a variety of metals, such as, alkali, alkaline earth metals, first transition metals, as well as Al, Sn, Pb, Sb, and the like. The presence of metals in heavy hydrocarbons during processing may cause corrosion, environmental pollution and poisoning of refining catalysts. These metals may also interfere in oil refining processes by causing excessive coke formation.
Crude oil is typically fractionated in a crude distillation zone to produce several hydrocarbon fractions, such as naphtha, diesel, vacuum gas oil, and resid. The metals in the crude tend to concentrate in the heavy hydrocarbon fractions such as atmospheric resid, vacuum resid, and gas oils. It is known to process heavier hydrocarbon fractions in thermal processes such as coking and visbreaking and in solvent de-asphalting processes to produce a heavy bottoms or coke product and lighter products, which may include a VGO-like fraction. Although the metals are concentrated in the heavy bottoms or coke product, the lighter products often require additional or specialized processing because they contain more metals relative to similar boiling range straight run fractions. Metals may also be removed by adsorption onto solid particles such as catalysts or adsorbents. Such particles may be used in conjunction with hydrotreating processes that also reduce the nitrogen and sulfur content of the heavier hydrocarbon fractions.
Various processes using ionic liquids to remove sulfur and nitrogen compounds from hydrocarbon fractions are known. U.S. Pat. No. 7,001,504 B2 discloses a process for the removal of organosulfur compounds from hydrocarbon materials which includes contacting an ionic liquid with a hydrocarbon material to extract sulfur containing compounds into the ionic liquid. U.S. Pat. No. 7,553,406 B2 discloses a process for removing polarizable impurities from hydrocarbons and mixtures of hydrocarbons using ionic liquids as an extraction medium. U.S. Pat. No. 7,553,406 B2 also discloses that different ionic liquids show different extractive properties for different polarizable compounds.
Liquid/Liquid Extraction of Metal Ions in Room Temperature Ionic Liquids, by Visser, Ann E, et al, SEPARATION SCIENCE AND TECHNOLOGY, 36(5&6), 785-804, (2001), Marcel Dekker, Inc., discloses the use of room temperature ionic liquids, specifically, 1-alkyl-3-methylimidazolium hexafluorophosphate, to separate metal ions from aqueous solutions.
There remains a need in the art for improved processes that reduce the metal content of vacuum gas oil (VGO).